1. Field of the Invention
The present invention relates to a sleep state measuring apparatus and a sleep state measuring method for detecting a biosignal which changes depending on the sleep state of a living body that gets on a mattress filled with fluid, amplifying, and estimating the sleep state based on the amplified biosignal.
2. Description of the Related Art
One of this kind of already-known apnea detecting apparatus detects the apnea in a user's sleep state, and the apnea detecting apparatus is equipped with the automatic gain control unit. In this apnea detecting apparatus, the pressure fluctuation which is propagated to the inside of an air mattress is detected from the user's body lying down on the air mattress filled with air as the biosignal by a microdifferential pressure sensor. The automatic gain control unit automatically controls the gain (amplification factor) of the detected biosignal and outputs the amplified biosignal to a filter equipped at the latter step (refer to Patent Document 1).
This filter is adjusted to heartbeat or respiration, for example. The filter adjusted to heartbeat extracts heartbeat signals and the filter adjusted to respiration extracts respiration signals. In addition, it is estimated whether the user on the mattress is in a particular sleep stage, or whether the user is in the apneic condition, by the latter procedure, from the fluctuation pattern of these heartbeat signals and respiration signals.
[Patent Document 1]
Japanese Unexamined Patent Application Publication No. 2000-271103 (Paragraph number [0017], [0020] to [0022], FIG. 1 and others).